UN chief Ban Ki-moon has expressed deep concern over a Russian aid convoy crossing the border into Ukraine without permission, asking all sides to exercise restraint and avoid escalation as any unilateral action could exacerbate an "already dangerous situation".

"While recognising the deteriorating humanitarian situation, any unilateral action has the potential of exacerbating an already dangerous situation in eastern Ukraine," Ban said in a statement from his spokesperson.

He asked all sides, particularly Ukraine and Russia, to continue to work together, in coordination with the international community, to ensure that humanitarian assistance reaches the most affected areas.

Ban reiterated that all sides should continue to exercise maximum restraint and avoid escalation.

The Secretary General said that he was encouraged by the announcement from Ukrainian President Petro Poroshenko that his country will do everything possible to prevent more serious consequences as a result of the convoy moving into Ukrainian territory.

Meanwhile in Ukraine, discussions with officials about the humanitarian needs of the people in the eastern part of the country have been very positive, Under-Secretary-General for Humanitarian Affairs Valerie Amos said at the start of a visit to see how aid delivery can be improved to the estimated 190,000 people currently displaced in the area.

"I would like all the parties that are involved in the conflict to remember that it is ordinary people who suffer the most when you have conflicts," she said.

Amos, who is also the world body's Emergency Coordinator, is on a four-day visit to the country to see first-hand the situation of some of the displaced communities, including in and around the city of Donetsk where she heads tomorrow.

"I hope that the political talks that are going on will lead to some kind of cessation of violence and a ceasefire," she said, stressing that the needs of the people affected by the fighting must be put first.

Last week, the Office for the Coordination of Humanitarian Affairs (OCHA) requested USD 33.3 million to continue to provide aid to the affected areas, including water and sanitation, shelter, health and education.

"Should the situation deteriorate further obviously we will need to review that plan," Amos said.

"In the discussions that I have had with the Ukrainian Government, the discussions have been very positive with respect to ways in which we can work together."